I have the same Problem with my serveraccount. I can also not login at maniaplanet.com with my account. It says invalid login or password. I can not create a new one because I dont know where to do so...

Don't panic. The first page is related to your MP3 account and the latter is MP4 account. At the moment of the update, all the accounts from MP3 were imported into the MP4 database. But after that, the two accounts are dissociated. So if you changed your MP3 password, it won't work on MP4. Nevertheless, the IG account is related to MP4. So all you have to do (since the "forgot password" button is not working on the MP4 page at the moment) is to reset your password from the game. To do this, when launching the game, before pressing "connection", just choose "use other profile", then "create profile", then "login" and then "I forgot my password".